Secondary batteries such as lithium secondary batteries and nickel-hydrogen batteries are preferably used as so-called portable power supplies in personal computers, mobile devices, etc., or as vehicle-driving power supplies. In particular, lithium secondary batteries that are lightweight and have high energy densities have become increasingly important as high output power supplies for use on vehicles such as electric automobiles, hybrid mobiles and the like (e.g. as power sources to drive motors connected to drive wheels of vehicles).
Typical examples of such secondary batteries include a hermetic battery (sealed battery) obtainable by sealing an electrode unit having a positive electrode and a negative electrode along with an electrolyte in a battery case. When charging this type of battery, in the presence of a defective battery or when a malfunction is caused by a charging device failure, the battery may be supplied with a higher current than usual and fall in an overcharged state. Upon such overcharge, the battery reactions proceed rapidly, gas is produced inside the sealed battery case to increase the internal pressure (gas pressure) of the battery case, and the abnormal internal pressure may cause deformation of the case, etc. To deal with such an abnormal occasion, as a conventional technique, a battery configuration has been suggested to comprise a current-blocking system that uses the pressure inside the battery case, which increases in association with abnormalities occurring in the battery, to cause deformation of a component so that the conduction is physically cut off to block the current.
Conventional examples related to a secondary battery comprising such a current-blocking system include Patent Document 1. The current-blocking system in this document comprises a current collector in a rectangular plate form connected to an electrode unit, and an invertible plate welded to the current collector. When the pressure inside the battery case (internal pressure of the case) increases, the internal pressure of the case causes the invertible plate to move away from the current collector. The current-blocking system is configured such that when the internal pressure of the case increases to a preset pressure value, the invertible plate breaks off part of the current collector including the welded joint and deforms in a direction to move away from the current collector. Thus, with the current collector partially breaking off and separating along with the invertible plate from the main body of the current collector, the current is blocked. Other conventional examples include Patent Document 2.